1. Field of the Invention
The present invention relates to a holding sealing material, a method for rolling the holding sealing material, and an exhaust gas purifying apparatus.
2. Discussion of the Background
Exhaust gas discharged from internal engines, such as diesel engines, contains particulate matter (hereinafter, also referred to as PM). The PM is becoming an issue these days because the PM is harmful to the environment and human bodies. The exhaust gas also contains harmful gases such as CO, HC, and NOx. Thus, these harmful gases are also becoming an issue due to their influence on the environment and the human bodies.
In such a situation, various exhaust gas purifying apparatuses are proposed which capture PM in exhaust gas and purify harmful gases. Examples thereof include an exhaust gas purifying apparatus including an exhaust gas treating unit including porous ceramic, such as silicon carbide or cordierite; a casing accommodating the exhaust gas treating unit; and a holding sealing material including an inorganic fibrous aggregate disposed between the exhaust gas treating unit and the casing. The holding sealing material of this type is disposed mainly for the following purposes: preventing damages on the exhaust gas treating unit which are caused by contact with the casing, which covers the periphery of the unit, due to vibration or impact generated upon driving of vehicles or other factors; and preventing leakage of exhaust gas from gaps between the exhaust gas treating unit and the casing.
The holding sealing material includes a mat including an inorganic fibrous material. In the plan view, the mat has a basic quadrangular shape consisting of long sides extending in the longitudinal direction and short sides substantially perpendicular to the long sides. A recessed portion is formed on one of the short sides, and a projected portion is formed on the other of the short side. The projected portion has a shape similar to the removed shape at the recessed portion. The mat is rolled around the periphery of the exhaust gas treating unit and the projected portion is made to fit to the recessed portion. Thereby, exhaust gas is prevented from leaking from the holding sealing material.
There has recently been an increasing demand for holding sealing materials which are excellent in heat-retention properties, that is, capable of sufficiently keeping an exhaust gas treating unit warm, so as to allow the exhaust gas treating unit to effectively exert the exhaust gas treating performance. In order to achieve such heat-retention properties, the exhaust gas treating unit and the casing are required to be widely separated from each other and a thick holding sealing material is required to fill the wide gap between the exhaust gas treating unit and the casing so as to sufficiently insulate heat. In addition, there has also been an increasing demand for higher repulsive force of the inorganic fibrous material, which is a factor for more securely holding the exhaust gas treating unit by the holding sealing material. In order to achieve such higher repulsive force of the inorganic fibrous material, the holding sealing material is required to have a higher weight (basic weight) per unit area.
The weight (basic weight) per unit area or the thickness of the holding sealing material may be increased by increasing the thickness of one mat. Alternatively, a multilayer mat is employed in which multiple mats each having the same basic weight and thickness as those of a conventional mat are combined and thereby the basic weight is increased.
In the case that the holding sealing material including multiple mats is rolled around the periphery of the exhaust gas treating unit, each mat is required to have an appropriate tension and the projected and recessed portions of each mat are required to smoothly fit to each other.
JP-A 2007-218221 and JP-A 2009-264186 each disclose the case in which multiple mats are used and fitting of projected and recessed portions of each mat is examined.
Claim 1 of JP-A 2007-218221 discloses that a laminate of mats is rolled around the periphery of a monolith without looseness in each mat and each mat is designed such that the length is adjusted so as to allow the fitting portions to fit to each other. Claim 3 of JP-A 2007-218221 discloses that the mats are fixed to each other such that at least one end of each mat freely moves in order to achieve the above feature.
JP-A 2009-264186 discloses a holding sealing material wherein the length of one mat in the longitudinal direction is longer than a mat at a lower position in the laminate, each of the mats are fixed by at least two fixing portions, and, in the side view, the at least two fixing portions are disposed at different positions in the longitudinal direction.
The contents of JP-A 2007-218221 and JP-A2009-264186 are incorporated herein by reference in their entirety.